U.S. patent application Ser. No. 06/920,118, filed Oct. 17, 1986 entitled "Automatically Operated Vacuum Feed and Hold Down Assembly For Camera System" discloses a daylight-operable vertical camera having an automatic vacuum feed and hold down system. The automatic vacuum feed and hold down system automatically withdraws and cuts a photosensitive sheet, transports the sheet to an exposure platen, centers the sheet, holds the sheet down onto the platen for exposure, and advances the exposed sheet for processing. The system includes a flexible transport belt extending between two rollers, with the belt being lifted away from the exposure platen of the camera during transport of the photosensitive material. Prior to exposure of the photosensitive material the belt is lowered onto the camera platen and air underneath the belt and photosensitive material is evacuated by applying a vacuum to a peripheral channel surrounding the platen.
Certain improvements to the structure and method of operation of the vacuum transport and hold down system disclosed and claimed in the foregoing application are set forth in U.S. patent application Ser. No. 07/149,647, filed Jan. 28, 1988 entitled "Automatic Vacuum Feed and Hold Down Assembly For Camera System". Among the improvements disclosed in the latter application is the inclusion of one or more transverse fabric ribs extending partially across the underside of the belt. The partially extending transverse ribs effectively "tent" the belt above the exposure platen to reduce the time required to evacuate air from beneath the belt during the hold-down phase of operation. The complete disclosures of the foregoing application Ser. Nos. 06/920,118 and 07/149,647 are hereby incorporated by reference, and familiarity with the contents of those disclosures is presumed.
The belt with rib construction has been found effective for its intended purpose, that is, reducing the length of time required for hold down evacuation, and is acceptable for most applications. However, vertical cameras are used, among other things, for lined screen exposures onto film. In this particularly demanding application, light is transmitted through the film and is reflected from the underside of the belt. It has been found that variations in reflectance from the underside of the belt often create retro-reflection shadow variation effects in the image recorded on the photosensitive film. It has further been found that there are variations in reflectance between the lower or bottom surface of the belt and the fabric ribs, which variations contribute to shadow variation effects. Of course, shadow variation effects are undesirable and detract from the quality and usefulness of the resulting film images.
Therefore, it is one object of the present invention to provide a vacuum transport and hold down belt that is not susceptible to retro-reflection shadow variation effects.
It is another object of the present invention to provide a vacuum transport and hold down belt that presents a substantially uniform bottom surface not susceptible to retro-reflection shadow variation effects.
It is a further object of the present invention to provide, in a vacuum transport and hold down system for an automatic camera, a belt that obtains expeditious evacuation of air from beneath the belt without being susceptible to retro-reflection shadow variation effects.
It is another object of the present invention to provide a vacuum transport and hold down belt that obtains expeditious evacuation of air beneath the belt without partial transverse ribs on the underside of the belt.
These and other highly desirable objects are accomplished by the present invention in an economical structure that obtains rapid evacuation of air beneath the belt without partial transverse ribs on the lower belt surface and without undesirable retro-reflection shadow variation effects.
Objects and advantages of the invention are set forth in part herein and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.
The invention consists of the novel parts, constructions, arrangements, combinations, steps and improvements herein shown and described.